I found Sharp Park to be a good site for a forum get together. Its not too far away, has a day use area and offer opportunities for people to camp if they wish at the park or adjacent River Bend. There is a creek adjacent to the park which will keep the kids amused, and where parents can supervise from under shady tree.

We also drove through Mt Tamborine. Overall we found the place real busy, just people everywhere and one issue is that parking is at a premium. Nearly everywhere we went we either got the last park or had to park in the bus parking bay etc. The facilities at the parks were also limited just a couple of tables. It would be difficult to accommodate a group of any real size. I have posted below some photos.

Look it would be good for small trips if you get their early to get a park.

Laheys Lookout (no toilets)

The Knoll

Cedar Creek Grove

Never argue with a fool! They drag you down to their level, and beat you with experience!